According to the prior art, a classic diagram of an arc welder with electronic control and power supply circuit is shown in FIG. 1.
This diagram provides a rectifier stage 1, followed by a bank of leveling capacitors 2 that supply a power transformer 4 by means of an inverter block 3 with high-frequency electronic switches.
The secondary winding of the transformer 4 is followed by a rectifier stage 5 and by an inductor 6 for leveling the output current, which is the current that circulates in a welding arc 7.
During operation, a welder with a diagram of this kind absorbs from the mains a current whose waveform has a shape of the kind shown in FIG. 2, which, as shown, has a high content of harmonics.
In this situation, the power factor is low, and in order to have a high output power on the arc it is necessary to draw a high RMS current value from the mains.
The high RMS factor and the high harmonic content of the absorbed current are a severe problem, particularly when power supply lines are not sized for this kind of load.
This occurs in particular when using welders in domestic environments, where the systems are sized for modest consumptions.
In this case the lines become dangerously warm and it is therefore necessary to limit the power delivered by the generator of the welder, with all the related consequences for the arc and for the possibility to perform welding.
If one did not proceed in this manner, the high intensity of the RMS current absorbed by the generator would cause the tripping of the safety thermal cutout of the system even though the useful power in output is lower than that of an equivalent resistive load.
A generator with this electrical diagram is also sensitive to variations in the input power supply voltage, particularly when the voltage decreases.
In this case, there is a marked decrease in the performance of the generator and therefore of the welder.
In view of these problems, generators for welders with additional stages have been developed so that they absorb on the power supply side a current that is as sinusoidal as possible.
In this manner, the generator is equivalent to a resistive load, and this allows to utilize all the available active power.
The additional stages also allow to adapt automatically the generator to the variation in mains voltage, thus ensuring the performance of the welder throughout its operating range.
A typical diagram with additional stages is shown, in its essential parts, in FIG. 3.
This diagram allows to notice, by comparing it with the diagram of FIG. 1, the addition of a stage 11, interposed between a rectifier block 12 and a leveling capacitor block 13.
Such additional stage 11 is known technically as a BOOST-type PFC and comprises an inductor 14, an electronic switch 15, and a diode 16, arranged as in FIG. 3.
The block 11, by means of an appropriate device 17 for controlling the switch 15, in addition to making the input current absorption practically sinusoidal as shown in FIG. 4, allows to keep constant the value of the voltage and the terminals of the leveling capacitor block 13 as the input voltage varies.
This also allows to optimize the size of the electronic power switches used in inverter block 18.
Another known generator is the one shown schematically in FIGS. 5, 6 and 7.
In this case there is a single input rectifier stage 21, capable of ensuring both sinusoidal absorption from the mains and automatic adaptation to input voltage fluctuations.
The input stage 21 is shown in greater detail in FIG. 6 in the case of a single-phase power supply and in FIG. 7 in the case of a three-phase power supply.
These circuits are illustrated in greater detail in WO 01/03874 by the same Applicant.
In this case, the generator is composed of a set of blocks that are designated, in FIG. 5, as an input rectifier stage 21, a level stage 22 with capacitors, an inverter stage 23 with electronic switches, a current transformer 24, and a power supply stage 25 for the welding arc 26.
The most important part of the generator is located in the input rectifier stage 21, shown in detail in FIGS. 6 and 7.
FIG. 6 shows a first detail of the input stage 21 related to a single-phase power supply generator.
In this circuit configuration, there is an inductor 27 that is directly connected to the mains input 28.
This inductor is followed by two diodes 29 and 30, which are mutually connected in opposition, each one being served by an electronic switch, designated by the reference numerals 31 and 32 respectively.
The outputs 33 and 34 supply the stage of the leveling capacitors 22.
In the case of a three-phase power supply, as shown in FIG. 7, there are three inductors, one for each phase, designated by the reference numerals 35, 36 and 37, which are directly connected to the mains 38.
Each one of the inductors is followed by a respective diode 39, 40 and 41, each of which is served by an electronic switch, designated by the reference numerals 42, 43 and 44 respectively.
This configuration allows to increase the overall efficiency of the system, since the power components used are reduced.
The problem of all known devices of the illustrated type is that two stages are always used in combination, i.e., a first input adaptation stage (PFC) and a second conversion stage that provides the welding inverter.
Moreover, there are two electronic control circuits dedicated respectively to the input adaptation stage (PFC) and to the inverter stage.